Magnetic ore-separator.



PATENTED OCT. 16, 1906.

Elm 833,169.

G. E. KNOWLES;

MAGNETFG ORE SEPARATOIL' APPLICATION FILED DBO. 5. 1901.

2 SHE-ETBSHEBT 1.

514 we 'm foz Camden E/(nawZes c1 flffo'zucl o d i 1-,

Wifmcoac PATENTED OCT. 16, 1906. v c. B. KNOWLES. MAGNETIC ORESEPARATOR.

APPLICATION FILED DEC. 5. 1901.

2 SHBETS-SHEBT 2.

0 l lll jk UNITED STATES PATENT o en.

YOAMDEN E. KNOWLES, OF JOPLIN, .MISSOURI, ASSIGNOR OF THREE- FOURTHS TOG. B. YOUNG, GEORGE T. COOLEY,-AN D GUY H. ELMORE, OF JOPLIN, MISSOURI.AND W. E. BRINKERHOFF, E. 'OKEEFE, AND JOSEPH HEREIN, OF UARTHAGE,MISSOURI.

MAGNETIC ORE-SEPARATQR.

' Application filed December To all whom it may concern:

Be it known that I, CAMDEN E; KNOWLES, 'a citizen of the United States,residing at Joplin, in the county of Jasper and State of Missouri, haveinvented certain new and use-1 ful Improvements in MagneticOre-Separators, of which the following is a specification.

The object ofmy invention is to provide means for the separation andclassification of ore of varying magnetic susceptibilities at a singleoperation; and my invention consists in the parts, combinations, andarrangements of parts hereinafter described and claimed.

In the drawings, Figure 1 represents a vertical longitudinal section ofa magnetic oreseparator embodying my invention; Fig. 2,

an enlarged sectional view of the poles of the magnet; Fig. 3, an endview of an electrical agitator; Fig. 4, a section on line 4 4 of Fig. 3;Fig. 5, an enlarged'section of the separating-belt, and Fig; '6 apartial top plan view corresponding to Fig. 5.

Reference-letters A and A enote, respectively, the north and south polesof an electromagnet; B, an a ron for feedin ore into the magnetic fieldBetween poles and A; C, an electric agitator for operating apronB; D, aseparating-belt E, E, and E drums or rollers carrying belt D; F, F, andF hoppers or bins for receiving the separated ore particles. The poles Aand A are the poles of an electromagnet having fiat pole-faces a set atan ,angle to each other, as shown in Figs. 1 and 2. B this arrangement afield of comparatively eeble strength is produced in region a, but whichgradually and continually increasesin strength till it reaches a maximumat a then gradually, but more abruptly, decreases to oint (L asindicated by the broken lines in ig. 2. I find that for most purposes anan le between pole-faces a of about thirty-five degrees is mostsatisfactory. Apron B is mounted in a slanting position parallel to facea of pole A and is su plied with pulverized ore from hopper b. t pointsI) apron B is given a pivotal bearing on rock-bars b, which are pivotedin station-. ary bearings 6 It extends into the imagnetic field, endingabruptly at or near the Specification of Letters Patent.

Patented Oct. 16, 1906.

5,1901. Serial No. 84,856.

link I) a ron B is connected with agitator G, by whic it is agitated tocause the ore to travel down its up er surface from the hopper 1; intothe fiel d between pole-pieces A and A. v a j The electrical agitator 0consists of a s in-, dle or sleeve 0, loosely mounted on sha cand'carrying pole-pieces c and Wire coil 6 Partially surrounding one endof sleeve 0 and fixed to shaft c is another sleeve 0, which is providedwith pole-pieces 0 mounted to pass within and in close proximity to polepieces 0 It will be noted that the passage .of an electric currentthrough coil 0 will constitute this apparatus an electromagnet, withpole-pieces c and 0 north or south poles, dependlng upon the directioninwhich the current is passed through coil 0 In the drawings pole-piecesc are indicated as being north poles and pole-pieces c as. south poles;

the pole-pieces are made north and which south poles. The coil 0 isconnected up in series with the coil which excites pole-pieces A and'A.One of the pole-pieces "c is connected to apron B by link I), while theother is connected to rod 0", which has a spring 0 bearing on one sideof stationary piece 0 and a stop 0 bearin on the other side thereof.Shaft c is rotate by means of a crossed-belt connection with shaft 0, soas to cause polepieces 0 to alternately approach. and recede rompole-pieces 0 As each pole-p1ece 0 passes each pole-piece c theattraction between them, due totheir op osite polarity, causes thepole-pieces c to e drawn alon with pole-pieces 0 against the resistance0 the spring 0 until the spring 0, together with the attraction of thenext approaching polepiece,'draws it back, thus causing a reciprocationof pole-pieces c and consequently of apron B, each time the pole iecesass.

The D belt-consists of a flexi le bo y portion d, carrying magneticpieces d, preferably of soft iron, which for simplicity I call secondamagnets. It is carried by drums or r0 lers E, E, and E so asto passarallel and in close proximity to face a of o e-piece A, between thelatter and apron ,until it point of maximum strength. Bymeans of jzontal direction before intersecting or, crossbut it 1s immaterial tothe operation which of I I ing the neutral line X X between the polethefield through whit it passes.

. ing both -a'ero'ssan'd l ngthwise of the belt D, g as shown Fig-6. Therows slanting 'cr'oss- .approaches the I feeble strength, but graduallypieces Aand A. As the magnetic pieces (1 pass across the faceofpole-piece A they be come, as it were, a part of pole-piece A andpartake of its magnetism with a degree of strength corresponding totheir positions in the field; In other Words, the lines of forceemanating from pole-piece A seek the path of least resistance topole-piecesA, and consequently pass through ieces d thus inducingmagnetism in pieces in proportion to the number of lines .per unit ofarea passing through them. An additional-eflect of this tendency of thelines to concentrate in the sec ndary magnets d" is to render theira'ctiial magnetism stron 'er than the "ortion of him each piece 11,b'e'ginnin with no magnetism, as it eld' ecomes an induced ma" et of'v'er an continually increasing in" strength as it progresses becomes avery powerful induced magnet when it reaches thelplace of maxirnu'mstren 'th in the fi ld. s

the magnets pass b'eyo'n the point of maximum strength V they retaintheir magnetism for a short time, but gradually lose it, becomin' weakerand weaker as they leave the field; ut, owing to their'moment'ary'retention of magnetism as 5 they pass from 'a stranger into a Weakerfield, 5

they carry with them into the Weaker field the magnetism of thepreceding stronger field; Thus'on the receding side of the field thesecondary magnets are always stronger than the field through which theypass.

Th fifi E, E, and are carried by Shafts 6L6, and- 0 mounted in suitablebearifigs- Shaft e is driven by b;elt e and iii t j drives shaft ethrough belt efin the direction The secon" ary magnets '11 are arrangein rows slant- 5 indicated byythe arrows in ii 1.

wise oi the belt insures the entry of an in-i (laced ma ih ity o drawaof et (1 into the region of maximum field simultaneously with thewithanother therefrom, thus preventing the jerking in the belt'w'hichwould result; from the sudden reduction of resistance on the belt if thesecondary magnets left the rei gion of maximum density of fieldunaccompanied bythe introduction of, others. The rows slantinglengthwise of the belt insure.

' arts of apron I orm treatment of the ore. A crossed belt 6 latter inthe direction indicated by the arrow align Bins I F, and F are set tocatch particles ialling' from belt D, bin F being connected the end ofapron B by, means of a flexible diaphragm or aipron f. Between bins Fand F and F and F are placed swinging partitions f and f -"for adjustingtheir mouths.

the'p'a'sjsage of secondary magnets over all B, and consequently a'uniconnectsshaft cwith shaft 0" to rotatefthc' In operationbelt e isoperated to drive drums E and E to draw belt D across the face ofpole-piece A, and an electric current I ispassed throughcoil c and thecoil forpolepieces -A and A. Rotation of drum E causes rota'tionof shaft0, and consequently agitation of apron B; and ore from hopper b iscaused to travel down the apron-toward polepieces A and A. As theseparticles pass into the outskirts or feeblest portion of the field thoseof greatest magnetic susceptibility are gradually worked to the top bythe combined action of the, ole-piece A and -the agitation of apron B. Te particles of the next greatest vmagnetic susceptibility seek aposition next un er the particles of greatest susceptibility,

and so on down through the thin sheet of ore I flowing down apron B, theparticles stratifying themselves in the order of their magneticsusceptibilities. Thus the non-magnetic and diamagnetic particles willseek the bottom strata Asthe particles proceed farther into thegradually increasing field those'most susceptible to magnetism become,as it were, lighter and lighter that is, have more and more tendency torise toward pole-piece A' until they reach a state where they may besaid to fairly float in the air immediately above the apron B, but sti ll under the influence of. its agitatidns. Here'any fine parti- (ties ofore of less magnetic su'sc'e tibility mechanically to them are s' akenoff by the agitation of apron B and fall back. 1mmediately afterwardwhen the particles have 1 reached an intensity of field corresponding totheir magnetic susceptibilities they are gently drawn up and cling tosecondary magnets '11, thus producing no violent or sudden action toentangle the particles. Further progress into the field produces a likeeffect on the particles of next greater magnetic susceptibility, and soon until the position of m t. mum density offi'eld is reached, when allthe magnetic particles ofo'r'e will-have been attracted to inducedmagnets d in the orderof their. magnetic susceptibilities It will be"noted that the ore particles leaving apron B at any instant of time, toattach themselves to any one secondary magnetmust n'ec'essarily be .ofthe same m-a' etic susceptibilit and free from mechanica' entanglementwit other ore particles. Thus the particles attaching to the secondarymagnets will reach them in the order of their magnetic susceptibilitiesand be arranged in layers or 'stratified .thereon in the inverse order.of their magmaximum strength; but after a momentary retention of themaximum magnetismthey begin to lose it and gradually decrease inmagnetism as they recedefi'om the point of maximum density of. field.When the decrease in strength of the secondary magnets reaches andpasses the point corresponding to'the magnetic susceptibility of theleast susceptible of the orep'articles, the force of gravity overcomestheir attraction to the magnets and they fall into bin F. Upon thefurther recession of ,the secondary magnets from the field they arefurther decreasedin magnetism, and further discharge of the attractedparticles takes place in the inverse order of their magneticsusceptibilities and at distances from the maximum density of fieldproportionate to their-magnetic susceptibilities. Thus it ,will be notedthat the d1scharge fromany one secondary'ma et at any instant of timemust 'necessarily e pari 't and the discharge from each secondary mag:net as it passes any'particular'position must be particles of the samemagnetic susceptibility. Particles varying from the least to medium*magnetic susceptibility will be deposited in b1n F and those varyingfrom medium to greatest magnetic susceptibility in bin F By adjustingthe swinging parti- "tion f the-mouth of bin F may be varied to insurethe prevention of the dropping of any of the particles of greatestmagnetic suscept1b1l1ty into bin F and swinging partition f 2 may beadjusted to vary the line of magnetic demarcation between the particlesfalling into bins F and F While I have illustrated bins adapted to makea division of the magnetic particles into but two cl asses,it is obviousthat by increasirig the number of bins the magnetic particles may bedivided into as many, classes, in accordance wit-h'their magneticsusceptibilities,

as desired;

the pole-piec Afchan es the direction of travel of thebelt D to 51chorizontal before it crosses theneutral line X X. Experience has shownthat it is desirable to maintain the travel of belt D on th'e same sideof neutral line X X, as the secondary magnets d seem to lose theirmagnetism too uickly for a nice separatioriif they cross said line. Inaddi tion to this effect the horizontal travel of the belt is desirable,inasmuch as it then affords the greatest ossible areafor the operationof gravity to e ect the discharge.

In order to obtain the best results, there should be a preliminaclassification or stratificatio'n of the ore be ore it enters the activezone of the field. The magnetic field should increase in attractivecapacity gradually and uniformly from the feed end to the discharge end,and provision should be made for the discharge of the non-magneticparticles just beyond the line of greatest intensity, so that thenon-magnetic particles may be discharged before any of the magneticarticles are freed from the domination of t e secondary magnets. *WhileI have illustrated the o posing ma etic surfaces as flat, which is t epreferred orm, it is obvious that the same result maybe obtained by anyarrangement which insures a gradual and practically uni' formconvergence from the feedend to a line closely adjacent to the dischar eend or by any arrangement'of the feed re ative to the magnetic surfaceswhich subjects the ores to the influence of magnetic attraction whichgradually increases from the feed end to approximately the point ofdischarge for the non-magnetic particles.

While I have illustrated and described the preferred form of apparatusembodying my invention, it: is obvious that the form' and constructionof-apparatus may be varied indefinitely without departing from thespirit of my invention. 1 therefore do. not Wish to be limited totheparticular construction disclosed; but Y What 'I claim, and desire tosecure by Letters Patent, is

1. In a magnetic separator, the combina-' tion of magnetic surfacesadapted to produce a magnetic field, said surfaces converging from thefeed to the discharge end and termi nating abruptly at the dischargeend; suitable provisions for feedv passin between the convergingsurfaces; and suita le provisions for discharge, substantially as s'ecified.

2. In a magnetic separator, t e combination of magnetic surfaces adaptedto produce a magnetic field, said surfaces converging from the feed tothe discharge'end and terminating abruptly at the discharge end suit- 1able provisions for feed passing between tlm convergin surfaces; andprovisions for dischargin t e non-magnetic particles at or im- I I Imediate y adjacent to the line of nearestap- Roller E mounted in closeproximity to proach of the magnetic surfaces, substan tially asspecified.

In a magneticseparator, the combinationof flat magnetic surfaces adaptedto pro- IIO duce a ma netic geld, said surfaces converging from t e feeto the dischar e end and terminating abruptly at the disc arge end;suitable provisions for feed passing between the converging surfaces;and suitable proyiisons for discharge, substantially as specie i 4. In amagnetic separator, the combination of magnetic surfaces adapted toproduce a magnetic field, said surfaces converging from the feed to thedischarge end and being arranged at an an le of substantially thirtyfivedegrees; suitaile provisions for feed passing between the conversurfaces; and suitable provisions for rfi s iilrarge, substantially asspecified.

' 5. In a magnetic separator, the combination of magnetic surfacesadapted to produce a magnetic field, said surfaces converging uniformlyfrom the feed to the discharge end; suitable provisions for feed passingbetween the converging surfaces; and suitable proiisglons fordischarge,substantially as speci- 6. In a ma etic separator, magnetic surfacesadapte to produce a magnetic field, said surfaces converging fromthefeed to the discharge end and terminating abruptly at the discharge end;a feeder adapted to car the ore into the field from the weaker enprovisions for dischargin the non-magnetic particles at or near the insofnearest approach; and a carrier provided withone or more secondarymagnets having a path of travel through the field, substantially asspecified.

7. In a magnetic separator, magnetic surfaces adapted to produce amagnetic field,

said surfaces converging from the feed to the discharge end andterminating abruptly at the discharge end, thereby constituting a pathof travel through field of gradually increasing intensity; a feederadapted to carry the ore into the field from the'weaker end; means foragitating thefeeder; provisions for discharging the nonmagnetic,particles at or near the line of greatest intensity; and a carrierprovided with one or more seconda ma nets having a the fie d,substantially as specified.

8. In a magnetic se arator, magneticsurfaces adapted topro ucc amagnetic field, said surfaces converging from the feed to the dischargeend and terminating abruptly at the discharge end, thereby producing afield of. graduallyincreasing intensity; a feeder adapted to carry theore into the field from the weaker end; provisions for discharging thenon-magnetic particles at or near the line of greatest intensity; and acarrier provided with one or more secondary magnets having -a path oftravel throughand extending beyond the active zone of the field,substantially as specified.

9. In a magnetic separator, magnetic surfaces adapted to produce amagnetic field,

' said surfaces converging from the feed to the:

' discharge end and terminatingabruptly at the discharge end, therebyproducing a field of gradually-increasingintensity; a feeder aratelydischargin the magnetic partic fied.

adapted to carr theore into the field from the. weaker en' means foragitating the feeder; provisions for dischargin the nonmagneticparticles at or near t he line of greatest intensity; and acarrierfprovided with one or more secondary magnets having a path oftravel through and extending be yond .the active zone of the field,substantially as specified.

10. The combination in a magnetic separator of magnetic surfacesconverging from the'feed to the dischar -e end, andconstitutingamagnetic field; a eeder assin through the field and adaptedto deEver t e orein proximity to one of thesurfaces; means for agitatingthe feeder thereby causing a stratification of the ores in the order oftheir magnetic susceptibilities; and provisions for septhe non-ma neticand es, substanti y as speci- 11. The combination in a magneticseparator of magnetic surfaces converging from the feed to the dischar eend, and constituting a magnetic field; a eeder passing through thefield and parallel to one of the surfaces; means for a 'itating thefeeder, thereby causing a strati cation of the ores inthe order of theirmagnetic susceptibilities; and provisions .for separately dischargingthe nonmagnetic and the magnetic particles, substantially' as specified.

12. The combination in a magnetic separator of ma the feed to t edischar e end,'thereby constituting a magnetic fiel said surfacesterminating abruptly at or near the line of greatest intensity; a feederin proximity to one of the surfaces; a carrier provided with one or moresecondary magnets, traveling between said etic surfaces converging fromsurface and the feeder, adapted to collect the magnetic particles asthey pass through the field, and to discharge them as they pass beyondthe field, substantially as specified.

' 13. The combination in a magnetic separator of magnetic surfacesconverging from the feed to the discharge end, thereby constituting amagnetic field; a feeder passing through the field and adapted todeliver the ore in proximity to one of the surfaces; means for agitatingthe feeder, thereby stratifying the ores in the order of their magneticsusceptibilities;- a carrier provided with one or more secondarymagnets, travelingbe-I tween said surface and the feeder, adapted tocollect the magnetic particles as they pass through the field, and todischarge them as they ass beyond the field, substantiallyas speci ed.

- 14. The combinationin a magnetic 'sepa-. rator of magnetic surfacesconverging from the feed t6 the discharge end, thereby consti-' tuting amagnetic field, said surfaces terminating abruptly at or near thedischarge end; a carrier provided with one or more secondfaces bemg setat an angle to each other, one above the other, and terminatingabruptly,

at the point of nearest approach, the upper makingan angle tothe'horizontal; a carrier provided with one or more secondary magnetsadapted to travel through the fie d from the side of widest divergenceabove the neutral line of the field andchanging its ath as it passesbeyond the surfaces to avoi crossing the neutral line; means for feedingthe ore in roximity to the upper surface, and means or dischar 'nthenon-magnetic, particles at or near the line of closest a roach of thesurfaces, substantially as spec ed.

16. The combination in a magnetic separator of conver ing magneticsurfaces set at an angle to eac other, one above the other, andterminating abru tly ator near the line of nearest approach, t e uppermaking an angle to the horizontal, said surfaces constitutmg a magneticfield; a carrier provided with one or more secondar ma ets adapted totravel. through the eld om the side of Widest divergence above theneutral line of the field andchanging its ath to the horizontal as itpasses beyon the surfaces to avoid crossing the neutral line; means forfeeding the ore in proximity to the upper surface; and means fordischargin the nonmagnetic particles at or near the line of closestapproach of the surfaces, substantially as specified. a i

17. The combination in a magnetic separator of converging magneticsurfaces set at an an le to eac other, one above the other, with the uper making an angle to the horizontal, an constituting a magnetic field;a carrier provided with one or more secondary magnets adapted to travelthrough the field from the side of Widest diver ence, above the neutralline of the field, paraTlel with the upper. surface, and changing itspathto the horizontal as it passes beyond the surfaces to avoid crossingthe neutral line pmeans for feeding the ore in proximity to the uppersurface ;-and means for discharging the nonmagnetic particles at or nearthe line of closest approach of the surfaces,- substantially asspecified. l a p 18 The combination in a magnetic separator of magneticsurfaces converging from the feed to the discharge end, thereby con-'minating abruptly at or near the discharge end; a carrier provided withone or more secondary magnets ada ted tov travel through the field, fromthe si( e of Widest divergence, on one side of the neutral line; afeeder carrying the ore into the field from the weaker side and on thesame side of the neutral line as the carrier; means for agitating thefeeder; and a discharge for the non-magnetic particles at or near theline of closest a roach of the surfaces, substantially as specl ed.

19. The combination in a magnetic separator ofconverging ma neticsurfaces arranged at an an le to eadh other, one above theiother, witht' he upper making an angle to the horizontal and adapted to produce amagnetic field; a carrier provided with'one'or more secondary magnetsadapted to travel through the field from the side of widest di vergenceabove the neutral line of the field, and changing its path as it passesbeyond the surfaces to avoid crossing the neutral line; a feederpassing-through the field and adapted to deliver the ore in proximity tothe upper surface; means for agitating the feeder; and means for discharin the non-magnetic particles at or near t e line of closest ap roach ofthe surfaces, substantially as specl ed.

20. The combination in a magnetic oreseparator of an electromagnethaving converging pole-faces set at an angle to each other, one abovethe other, with .the upper one making an angle with the horizonta aflexible belt carrying secondary magnets and ace of the magnet, thenchanging to a orizontal direction. before crossing the plane bisectingthe angle between the polefaces; a feed-a ron extending into'the an 1ebetween the po e-faees under the belt an above the lane bisectin the anle between thepoleaces; means for sup fying the apron with ore; binslocated un er the horizontal portion of the belt; and means fordischarging the material remaining on the apron in the re 'on of closestproximity of the pole-faces suhstantially as specified.

21. The combination in-a'magnetic oreseparator of an electr omagnethaving con- .verging pole-faces set at anangle to each other, one abovethe other, with the upper one making an angle with the horizonta aflexible belt carrying secondary magnets and assing along the surface-ofthe upper o1eace of the magnet, then changing to a iorizontal directionbefore crossing the plane bisecting-the angle between the pole-faces; afeed-a ron extending into the an le between the po e-faces under thebelt'an I abo veithe plane bisecting the angle between the poleaces;means or supp yin the apron w1th ore; bins located under the llorizontalportion of the belt; means for discharging the matestituting a magneticfield, said surfaces ter Ibo assing along the surface of the upperolerial remaining on the apron in'the region of 'closest proximity ofthe pole-faces; and

means for' agitating the apron, substantially as specified.

22. The combination in a magnetic orese ar'ator of an electromagnethaving two p0 e-fa'ces set at an angle to each other and one above theother, with the upper one makin an angle with the horizontal; a flexiblebe t carrying secondary magnets and passing along the surface of theupper pole-face, then changing to a horizontal direction before crossmthe plane bisecting the an le between t e pole-faces; a feedapron un erthe belt and above the plane bisecting the angle between the pole-faces;means for supplying the apronwlth ore; bins loc'at'edunder thehorizontal portion of the belt; means for discharging the materialremaining on the apron in the region of closest proximity of thepolefaces; and electrical means for a 'tating the apron, 'connected inseries with t e excitingcoils 'of the electromagnet, substantially asspecificed.

23. The combination in a magn'etie oreseparator of an electromagnetadapted to produce a magnetic field; means for effecting a magneticseparation of ore in said field; feeding mechanism for feedingthe' oreinto'said fie d poles of o p'osite polarity rotatably mo'u'nted on saishaft, spring-held to permit a limited movement; a connection betweenthe latter poles and the apron, the magnets being connected in series;and means for rotating the shaft, substantially as specified.

rator of two opposing magnetic surfaces set at an angie to each other; aexiblebeltcarrying secondary magnets arranged in rows slanting bothcrosswise and lengthwise of the belt; means for passing said beltbetween'said surfaces from the open side "of their angle; a

e combination in.a magnetic sepafeeder adapted to deliver the orebetween said surfaces from the open side of their 'angle; and means fordischarging non-magnetic articles at 'or near the region where saidsuraces most nearly approach, substantially as specified;

26. The combination in a magnetic separator of two opposing magneticsurfaces set at an angle to each other; a flexible belt carryingsecondary magnets arran' ed'in rows s anting both crosswise and lengt''wise fof'the belt; means for passing said belt between said surfacesfrom the open side of their angle; a feeder adapted to deliver orebetween said surfaces from the open side of their anle'; means fordischarging non-magnetic pan icles at or near the'region where saids'uir: faces most nearly approach; and a series of bins adapted toreceive the magnetic parti cles as they are released from the secondarymagnets, substantially as specified.

2,7. The combination in a magnetic separator of a field composed offlatconvergmg magnetic surfaces; a feeder adaptedto de-- liver or'e inproximity to and parallel with one of the surfaces; means for agitatingthe feeder; provisions fordischargin the nonmagnetic particles at ornear the line of nearest approach of the surfaces; -a flexible belt Iprovided with secondary magnets arranged:

to travel between the feeder and the nearer I surface and beyond thesurfaces; and a series of bins for collecting the magnetic particle's,substantially as specified.

28. The combination in separator of an electromagnet adapted to producea magnetic field; a field-apron extend-' ing into said field, anelectric a tater, for agitating the apron, having its coll connected ina magnetic oreseries with the coil of thefield-magnet; a

